1. Field of the Invention
The present invention generally relates to semiconductor devices, and more specifically, to a semiconductor device having an electrode connection structure where a convex-shaped electrode provided on a main surface of a semiconductor element is connected and fixed to a conductive layer selectively provided on a main surface of a supporting board.
2. Description of the Related Art
A semiconductor device where a semiconductor element is mounted on a supporting board in a so-called face down state has been used. In the semiconductor device, a basic material of the supporting board is insulation resin such as glass-epoxy resin. The supporting board is formed by laminating plural wiring boards having surfaces where conductive layers made of copper (Cu) or the like are selectively provided. A convex-shaped electrode provided on a main surface of a semiconductor element is connected to the conductive layer selectively provided on the main surface of the supporting board. An outside connection terminal such as a spherical-shaped electrode terminal is provided on the surface of the conductive layer selectively provided on the other main surface of the supporting board.
Under this structure an gold (Au) ball is pressure-fixed and connected on an outside connection terminal pad on the main surface of the semiconductor element by a wire ball bonding method, so that the convex-shaped outside connection terminal having both a base part and a part projecting from the base part is formed. A flattening process is, if necessary, applied to the part projecting from the base part. A terminal having such a structure, namely the terminal formed by a wire made of soft metal such as gold (Au) and having the base part and the part projecting from the base part is called a ball bump.
Since such a terminal having the base part and the part projecting from the base part has a large surface area, the terminal is easily connected and fixed to the conductive layer on the supporting board by a conductive member such as solder.
Such a connection structure can be realized at relatively low cost. Therefore, this structure is applied to a relatively small-sized semiconductor element having several through several hundreds outside connection terminals. See Japanese Patent Application Publication No. 2-163950 and Japanese Patent Application Publication No. 10-117065.
In order to form the semiconductor device, after a conductive member such as solder is selectively provided on a surface of the conductive layer provided on the main surface of the supporting board, the convex-shaped outside connection terminals of the semiconductor element come in contact with the conductive member. In this state, the conductive member is heated to a temperature equal to or greater than the melting point so as to be melted.
After that, the temperature is decreased so as to be equal to or less than the melting point of the conductive member such as a room temperature, so that the conductive member is solidified. As a result of this, the convex-shaped outside connection terminal of the semiconductor element is mechanically and electrically connected to the conductive layer on the supporting board.
However, since processes for increasing or decreasing the temperature are applied in this example as discussed above, stress based on the difference between coefficients of thermal expansion of the semiconductor element and the supporting board is concentrated on the conductive member between the convex-shaped outside connection terminal of the semiconductor element and the conductive layer on the supporting board. As a result of this, a crack may be generated in the conductive member so that an electrical connection between the convex-shaped outside connection terminal of the semiconductor element and the conductive layer on the supporting board is broken.
Even if a crack is not generated just after the temperature is decreased, the stress is concentrated on and remains in the conductive member between the convex-shaped outside connection terminal of the semiconductor element and the conductive layer on the supporting board. Therefore, a crack may be generated due to change of the temperature or vibration in the manufacturing process right after this process.
In addition, even if a crack is not generated in the manufacturing process, a crack may remain when the semiconductor device is actually working, so that reliability of the semiconductor device may be degraded.
In a case where a thin board such as a both surfaces wiring board is used as the supporting board, the board may have a large amount of warpage. Therefore, in this case, a crack may be generated.